1. Field of the Invention
The present invention relates to a high voltage MOS-gated power device, and to a related manufacturing process.
2. Discussion of the Related Art
MOS-gated power devices with breakdown voltages between 300 and 1000 V have a high output resistance (or xe2x80x9conxe2x80x9d resistance) due mainly to the epitaxial drain layer resistance that is necessary for the high voltage applied, and depends on the doping concentration of the epitaxial layer itself.
On the other hand, if, in the attempt to increase the integration density it is desired to reduce the distance between the elementary functional units (cells or stripes) without increasing the output resistance of the MOS-gated power device, it is necessary to increase the doping concentration of the common drain layer. This, however, results in a reduction of the breakdown voltage of the MOS-gated power device.
In order to obtain MOS-gated power devices with a low output resistance and a high breakdown voltage, it is possible to produce power devices with drain layers comprising many sub-layers with different doping concentrations (MultiDrain devices, MDMOS).
Another known technique is described in U.S. Pat. No. 5,216,275 and in U.S. Pat. No. 5,438,215, wherein the common drain layers beneath the body regions of the elementary functional units are constituted by columns of the N conductivity type, alternated to body xe2x80x9cpocketsxe2x80x9d of the P conductivity type. The above mentioned structure is obtained by a manufacturing process comprising trench etching and filling steps, and such a process is very complex because the drain thickness is comprised between 20 and 100 xcexcm whereas the width of the cells or stripes is about 5-10 xcexcm.
In view of the state of the art described, it is an object of the present invention to provide a high voltage MOS-gated power device with a low output resistance.
According to the present invention, these and other objects are achieved in a MOS-gated power device comprising a plurality of elementary functional units, each elementary functional unit comprising a body region of a first conductivity type formed in a semiconductor material layer of a second conductivity type, a plurality of doped regions of a first conductivity type formed in said semiconductor material layer, each one of said doped regions being disposed under a respective body region and being separated from other doped regions by portions of said semiconductor material layer.
As a result of the present invention, and specifically due to the presence of the doped regions of a first conductivity type under the body regions of the elementary functional units, a MOS-gated power device is provided which, for a given breakdown voltage, has a common drain layer with a lower resistivity than that which would be necessary in a conventional MOS-gated power device with the same breakdown voltage.
Moreover, the doped regions under the body regions of the elementary functional units are able to withstand the high voltage in which the power device operates.